If there's one thing we've learned about pop music over the last half-century, it's that while the boy band might not always be at pop's center, it's somewhere orbiting around it -- and will be back soon enough.

From the early '70s to the mid '80s to the late '90s to the early '10s to now, boy bands have seemingly always arrived in American pop culture in waves, crashing onto our shores suddenly and dramatically. Sometimes they come from elsewhere -- the U.K., Korea, even nearby Latin America -- and sometimes they spring up locally, from unexpected hotspots like Gary, Indiana; Tulsa, Oklahoma; Orlando, Florida. But each time they come, pop music is never the same afterwards -- nor are the lives of tens of millions of screaming young'ns whose early adolescences will come to be defined by their songs.

This week, Billboard is celebrating this venerated pop institution with a week of boy band-related coverage, starting with our list of the 100 Greatest Boy Band Songs of All Time -- spanning nearly the entire Hot 100 era, and recognizing the absolute tops in innocent male harmonies and synchronized dance moves.

But what is a boy band, you may ask? Ask any two music fans that question and you might get answers as varied as if you asked a 47-year-old FM DJ and a 19-year-old SoundCloud rapper to define "hip-hop." There are common elements most everyone can agree on as being obviously boy band-core, natch: the aforementioned harmonies and dancing, as well as matching outfits, major pop choruses, a puppet-string-pulling svengali behind the scenes, a general sense of ridiculousness (and a relative lack of self-consciousness), and of course, youth.

But aside from basic membership -- by pretty much all definitions, boy bands need to have at least three members and be all male -- there's no one unifying factor that links every boy band in history; name any classic trope of the format and we can name at least two obvious boy bands who it doesn't apply to. If anything, what really unites boy bands throughout history comes not in their conception, but in their reception: How young, rabid and ear-splittingly friggin' loud was their fanbase? If the answer is at least "very" to all three of these, you're already 80 percent of the way there.

Ultimately, we took every boy band argument on a case-by-case basis, and came to some difficult conclusions. Some groups, like 5 Seconds of Summer, were deemed eligible even though their structural makeup wasn't classically boy band, because the way they were marketed and fan-devoured was. Others, like The Beatles -- yes, The Beatles -- were given the boy-band OK for early stretches of their career, but a hard cutoff was instituted for after they matured and self-actualized as just a "band." And some, like modern self-identifying "boy band" BROCKHAMPTON, were just a little too far outside the conventional sound of a boy band for us to make the mental leap -- for now, anyway. (To see us hash out the "Are They a Boy Band?" arguments for all three of these cases and several others, click here.)

But enough trying to be Webster's, let's get to the songs -- with a Spotify playlist of all 100 of 'em at the bottom. They're original, they're the only ones, they're (occasionally, unthreateningly) sexual, and they're definitely everything you need.